Origin of observed changes in 14N hyperfine interaction accompanying R → T transition in nitrosylhemoglobin
Origin of observed changes in 14N hyperfine interaction accompanying R → T transition in nitrosylhemoglobin
复制标题
亚硝基血红蛋白中伴随 R→T 转变的 14N 超精细相互作用观察到的变化的起源
DOI：
10.1073/pnas.76.10.4842
复制
发表时间：
1979
影响因子：
11.1
通讯作者：
T. P. Das
中科院分区：
文献类型：
--
作者：
S. K. Mun;Jane C. Chang;T. P. Das
摘要
在八种不同结构形式的亚硝基血红蛋白的电子分布的理论研究进行了研究的变化，观察到的14 N超精细相互作用的影响下，肌醇六磷酸或改变pH值的R到T结构的过渡。研究的八种形式中的四个包括质子化和去质子化的Npros在近端咪唑配体与线性和弯曲的Fe-N-O结构。另外两种形式具有直的Fe-N-O结构和拉伸0.5和1.0的Fe-Im键。我们研究的另外两个体系是具有弯曲和直的Fe-N-O结构的五配体NO-血红素。我们的研究表明，能级的安排没有显着不同的所有结构，未成对电子总是占据一个反键轨道与dz 2对称性。具有线性或弯曲Fe-N-O结构的质子化和去质子化系统显示NO基团的14 N核和近端咪唑的Ne原子的实质性超精细相互作用，表明在所有四种情况下预期的9线电子自旋共振超精细图案（R结构）。另一方面，Fe-Im键的延伸产生14 Ne超精细相互作用的相当大的减少，表明超过1.0 A的延伸将提供接近于五配体NO-血红素系统的3线超精细图案。因此，我们的结果为文献中提出的Fe-Ne键严重延伸或断裂的模型提供了定量支持，该模型用于解释亚硝基血红蛋白α链的R-到-T转变。
Abstract
Theoretical investigations of electronic distributions in eight different structural forms of nitrosylhemoglobin were carried out to study the changes in 14N hyperfine interaction observed with the transition from R to T structures under the influence of inositol hexaphosphate or changing pH. Four of the eight forms studied consisted of protonated and deprotonated Npros in the proximal imidazole ligand with linear and bent Fe—N—O structures. Two other forms had a straight Fe—N—O structure and Fe—Im bond stretched by 0.5 and 1.0 A. The other two systems we have studied are five-liganded NO-heme with bent and straight Fe—N—O structures. Our investigations show that arrangements of energy levels did not differ significantly among all the structures, the unpaired electron always occupying an antibonding orbital with dz2 symmetry. The protonated and deprotonated systems with either linear or bent Fe—N—O structure showed substantial hyperfine interaction of the 14N nuclei of the NO group and the Ne atom of the proximal imidazole, indicating that a 9-line electron spin resonance hyperfine pattern (R structure) would be expected in all four cases. On the other hand, the extensions of the Fe—Im bond produce a sizeable decrease in the 14Ne hyperfine interaction, indicating that an extension beyond 1.0 A would provide a 3-line hyperfine pattern close to that found for the five-liganded NO-heme system. Our results thus provide quantitative support for the model of severe extension or cleavage of the Fe—Ne bond proposed in the literature for explaining the R-to-T transition of the α-chain of nitrosylhemoglobin.